I got the idea early on in using calibre that I should do a mobi-to-mobi conversion after I add a book that started out as a prc and has since been stripped of DRM. I always do it, and things work great, but I'm not sure why I do it or where I got the idea that I should.

Can anybody shed any light on it? Is it a useless step? Once I do that, I usually make an epub version, too, so I'll be able to read the book on both my sony and my kindle.

I also typically do a mobi to mobi conversion when adding books to my library.

In addition to reasons previously noted. doing the conversion also adds the chapter navigation feature for the Kindle (if the book doesn't already include it -- which many do not). It also allows changing the justification if desired -- I personally dislike full-justification on small screens w/o hyphenation.